The present invention relates generally to fiber optic light couplers and, more particularly, to fiber optic coupling assemblies for directionally inserting light into optic fibers or optical waveguides.
As is well known, an optical fiber or optical waveguide is constituted by a core with a refractive index N surrounded by a cladding with an index n lower than N and that it guides, in the core, light which is introduced at one end thereof to the other end essentially by a process of internal reflection.
In a typical arrangement, such as in a two way fiber optic light coupling assembly, light is introduced into one end of the fiber or waveguide through a light separator or beam splitting lens system and travels in a forward direction through the fiber core to the exit end of the fiber where, for example, it is reflected off a movable or deformable mirror back into the fiber or waveguide and returns in the reverse direction back to the entrance end of the fiber or waveguide where it exits the fiber and is directed by the light separator or beam splitter to a detector such as a photodiode. However, it has been found that in all such prior arrangements, a problem is presented in that the returning light signal directed toward the detector is obscured or significantly masked as a result of the optical interface reflections generated primarily at the light entrance end of the fiber and off the light separator or beam splitting lens itself.
Accordingly, it is an object of the present invention to provide a solution for this problem by providing a fiber optic coupler which directs injected light essentially unidirectionally from a position of introduction of the light into the core intermediate the ends of the fiber or waveguide toward the exit end of the fiber or waveguide so that interference with the returning light signal at the end of the fiber at which the detector is positioned will be essentially eliminated.